E26 Transformation-specific Research Articles

TMPRSS2:ERG Gene Fusion Might Predict Resistance to PARP Inhibitors in Metastatic Castration-resistant Prostate Cancer.

The emergence of novel DNA damage repair (DDR) pathways in molecular-target therapy drugs (MTTD) has shown promising outcomes in treating patients with metastatic castration-resistant prostate cancer (mCRPC). About 25% of mCRPC patients have actionable deleterious aberrations in DDR genes, primarily in the homologous recombination (HR) pathway. However, the response rate in patients with BRCA1/2 or mutations in HRR-related genes is only 45%-55%, when exposed to poly ADP ribose polymerase (PARP) inhibitor-based therapy (PARPi). A frequent characteristic feature of prostate cancer (PC) is the occurrence of genomic rearrangement that affects the transmembrane protease serine 2 (TMPRSS2) and E26 transformation-specific (ETS)- transcription factor-related gene (ERG). In this study, a total of 114 patients with mCRPC had their RNA and DNA sequenced using next-generation sequencing. Based on their genetic profile of deleterious gene alterations of BRCA1/2 or ATM, six patients were selected for PARPi. Patients with TMPRSS2:ERG gene fusion and homozygous alteration in ATM or BRCA2 (n=2) or heterozygous alterations (BRCA1 or BRCA2) and lack of TMPRSS2:ERG gene fusion (n=2) did not show clinical benefit from PARPi (treatment duration <16 weeks). In contrast, patients (n=2) without TMPRSS2:ERG gene fusion and homozygous deleterious alterations in ATM or BRCA2 all had clinical benefit from PARPi (treatment duration ≥16 weeks). The TMPRSS2:ERG transcript product might be used as a PARPi resistance biomarker.

ETS Transcription Factors in Immune Cells and Immune-Related Diseases.

The development, differentiation, and function of immune cells are precisely regulated by transcription factors. The E26 transformation-specific (ETS) transcription factor family is involved in various physiological and pathological processes by regulating cell proliferation, differentiation, and apoptosis. Emerging evidence has suggested that ETS family proteins are intimately involved in the development and function of immune cells. This review summarizes the role of the ETS family in immune cells and immune-related disorders. Seven transcription factors within the ETS family, including PU.1, ETV5, ETV6, ETS1/2, ELK3, and ELF1, play essential roles in the development and function of T cells, B cells, macrophages, neutrophils, and dendritic cells. Furthermore, they are involved in the occurrence and development of immune-related diseases, including tumors, allergies, autoimmune diseases, and arteriosclerosis. This review is conducive to a comprehensive overview of the role of the ETS family in immune cells, and thus is informative for the development of novel therapeutic strategies targeting the ETS family for immune-related diseases.

A novel role of ETV6 as a pro-viral factor in host response by inhibiting TBK1 phosphorylation

E26-transforming specific (ETS) variant 6 (ETV6) is a transcription factor regulating the expression of interferon stimulating genes (ISGs) and involved in the embryonic development and hematopoietic regulation, but the role of ETV6 in host response to virus infection is not clear. In this study, we show that ETV6 was upregulated in DF-1 cells with poly(I:C) stimulation or IBDV, AIV and ARV infection via engagement of dsRNA by MDA5. Overexpression of ETV6 in DF-1 cells markedly inhibited IBDV-induced type I interferon (IFN-I) and ISGs expressions. In contrast, knockdown, or knockout of ETV6 remarkably inhibited IBDV replication via promoting IFN-I response. Furthermore, our data show that ETV6 negatively regulated host antiviral response to IBDV infection by interaction with TANK binding kinase 1 (TBK1) and subsequently inhibited its phosphorylation. These results uncovered a novel role of ETV6 as a pro-viral factor in host response by inhibiting TBK1 phosphorylation, furthering our understandings of RNA virus immunosuppression and providing a valuable clue to the development of antiviral reagents for the control of avian RNA virus infection.

An intricate regulatory circuit between FLI1 and GATA1/GATA2/LDB1/ERG dictates erythroid vs. megakaryocytic differentiation.

During hematopoiesis, megakaryocytic erythroid progenitors (MEPs) differentiate into megakaryocytic or erythroid lineages in response to specific transcriptional factors, yet the regulatory mechanism remains to be elucidated. Using the MEP‑like cell line HEL western blotting, RT‑qPCR, lentivirus‑mediated downregulation, flow cytometry as well as chromatin immunoprecipitation (ChIp) assay demonstrated that the E26 transformation‑specific (ETS) transcription factor friend leukemia integration factor 1 (Fli‑1) inhibits erythroid differentiation. The present study using these methods showed that while FLI1‑mediated downregulation of GATA binding protein 1 (GATA1) suppresses erythropoiesis, its direct transcriptional induction of GATA2 promotes megakaryocytic differentiation. GATA1 is also involved in megakaryocytic differentiation through regulation of GATA2. By contrast to FLI1, the ETS member erythroblast transformation‑specific‑related gene (ERG) negatively controls GATA2 and its overexpression through exogenous transfection blocks megakaryocytic differentiation. In addition, FLI1 regulates expression of LIM Domain Binding 1 (LDB1) during erythroid and megakaryocytic commitment, whereas shRNA‑mediated depletion of LDB1 downregulates FLI1 and GATA2 but increases GATA1 expression. In agreement, LDB1 ablation using shRNA lentivirus expression blocks megakaryocytic differentiation and modestly suppresses erythroid maturation. These results suggested that a certain threshold level of LDB1 expression enables FLI1 to block erythroid differentiation. Overall, FLI1 controlled the commitment of MEP to either erythroid or megakaryocytic lineage through an intricate regulation of GATA1/GATA2, LDB1 and ERG, exposing multiple targets for cell fate commitment and therapeutic intervention.

Transcription Factors in Prostate Cancer: Insights for Disease Development and Diagnostic and Therapeutic Approaches.

Transcription factors (TFs) are proteins essential for the regulation of gene expression, and they regulate the genes involved in different cellular processes, such as proliferation, differentiation, survival, and apoptosis. Although their expression is essential in normal physiological conditions, abnormal regulation of TFs plays critical role in several diseases, including cancer. In prostate cancer, the most common malignancy in men, TFs are known to play crucial roles in the initiation, progression, and resistance to therapy of the disease. Understanding the interplay between these TFs and their downstream targets provides insights into the molecular basis of prostate cancer pathogenesis. In this review, we discuss the involvement of key TFs, including the E26 Transformation-Specific (ETS) Family (ERG and SPDEF), NF-κB, Activating Protein-1 (AP-1), MYC, and androgen receptor (AR), in prostate cancer while focusing on the molecular mechanisms involved in prostate cancer development. We also discuss emerging diagnostic strategies, early detection, and risk stratification using TFs. Furthermore, we explore the development of therapeutic interventions targeting TF pathways, including the use of small molecule inhibitors, gene therapies, and immunotherapies, aimed at disrupting oncogenic TF signaling and improving patient outcomes. Understanding the complex regulation of TFs in prostate cancer provides valuable insights into disease biology, which ultimately may lead to advancing precision approaches for patients.

High UV damage and low repair, but not cytosine deamination, stimulate mutation hotspots at ETS binding sites in melanoma

Noncoding mutation hotspots have been identified in melanoma and many of them occur at the binding sites of E26 transformation-specific (ETS) proteins; however, their formation mechanism and functional impacts are not fully understood. Here, we used UV (Ultraviolet) damage sequencing data and analyzed cyclobutane pyrimidine dimer (CPD) formation, DNA repair, and CPD deamination in human cells at single-nucleotide resolution. Our data show prominent CPD hotspots immediately after UV irradiation at ETS binding sites, particularly at sites with a conserved TTCCGG motif, which correlate with mutation hotspots identified in cutaneous melanoma. Additionally, CPDs are repaired slower at ETS binding sites than in flanking DNA. Cytosine deamination in CPDs to uracil is suggested as an important step for UV mutagenesis. However, we found that CPD deamination is significantly suppressed at ETS binding sites, particularly for the CPD hotspot on the 5' side of the ETS motif, arguing against a role for CPD deamination in promoting ETS-associated UV mutations. Finally, we analyzed a subset of frequently mutated promoters, including the ribosomal protein genes RPL13A and RPS20, and found that mutations in the ETS motif can significantly reduce the promoter activity. Thus, our data identify high UV damage and low repair, but not CPD deamination, as the main mechanism for ETS-associated mutations in melanoma and uncover important roles of often-overlooked mutation hotspots in perturbing gene transcription.

ETV7 promotes colorectal cancer progression through upregulation of IFIT3

Members of the E26 transformation-specific (ETS) variant transcription factor family act as either tumor suppressors or oncogenic factors in numerous types of cancer. ETS variant transcription factor 7 (ETV7) participates in the development of malignant tumors, whereas its involvement in colorectal cancer (CRC) is less clear. In this study, The Cancer Genome Atlas (TCGA) and immunochemistry staining were applied to check the clinical relevance of ETV7 and interferon-induced protein with tetratricopeptide repeats 3 (IFIT3) in CRC patients. Overexpression and knockdown of ETV7 and IFIT3 were conducted by transfecting the cells with pCDNA3.1 plasmids and siRNAs, respectively. Western blotting was used to detect the protein expression of ETV7 in CRC cells. Cell Counting Kit-8, cell colony formation, and Transwell assays, as well as flow cytometry, were used to evaluate the proliferation, migration, cell cycle, and apoptosis of CRC cells. Furthermore, western blotting, RT-qPCR, and luciferase assay were used to explore the regulation of ETV7 on IFIT3. Rescue assay was used to investigate the significance of ETV7/IFIT3 axis on CRC progression. We found that ETV7 was upregulated in CRC tissues and cells. Overexpression of ETV7 stimulated the proliferation, migration, and cell cycle amplification, and reduced the apoptosis of CRC cells. Downregulation of ETV7 exerted the opposite effect on CRC cell progression. Moreover, we demonstrated that ETV7 stimulated the transcription activity, the mRNA and protein expression of IFIT3 in CRC cells. There was a positive correlation between ETV7 and IFIT3 in CRC patients. IFIT3 knockdown reversed the promotive effect exerted by overexpression of ETV7 on the amplification and migration of CRC cells. By contrast, overexpression of IFIT3 blocked the inhibitory effect of ETV7-targeting siRNA. In summary, ETV7 induces progression of CRC by activating the transcriptional expression of IFIT3. The EVT7/IFIT3 axis may be a novel target for CRC therapy.

CCRG-05. A UNIFYING AND SELF-REINFORCING MECHANISM OF TUMOR IMMORTALITY IN TERT PROMOTER MUTANT CANCERS

Abstract Telomerase Reverse Transcriptase promoter mutations enable tumor cell immortality in millions of cancer patients annually. While prior therapies targeting telomerase lacked tumor selectivity and were poorly tolerated, TERT promoter mutations and their regulation present a unique opportunity for tumor specific reversal of cellular immortality. The two hotspot mutations, G228A and G250A, generate identical de novo E26 transformation specific (ETS) transcription factor binding sites. However, the 28 ETS factors share a similar binding site preference, raising the question of whether all ETS factors can reactivate TERT. In glioblastoma and a few other cancers, we have shown the de novo ETS site along with a nearby native ETS site (ETS-195/200) recruit one ETS factor, the GA-binding protein (GABP) tetramer, to reactivate TERT. This GABP-mediated mechanism may be restricted to specific cancer types and the two hotspot mutations or could be widely relevant to any cancer with a de novo ETS TERT promoter mutation. We have found that the GABP tetramer activates 6 distinct mutant TERT promoters across 16 different cancer types. However, TERT expression is maintained in most tetramer depleted tumor cells as the tetramer is serially replaced by GABP dimers and weakly by a paralogous tetramer complex that increase following disengagement of GABP tetramer-mediated negative feedback loops. Elimination of both the tetramer and dimer reinstates epigenetic repression of TERT, shortens telomeres, and prevents cancer cell division. However, some knockout cancer cells avoid this fate through weak activation of TERT by the paralogous GABP tetramer complex. The compensatory maintenance of TERT expression can be overcome with a dominant negative GABPB1, leading to TERT silencing, evidenced by gene expression and non-invasive metabolic imaging correlates, and telomere shortening in TERT promoter mutant glioblastoma. We are currently investigating the delivery of this dominant negative to tumor cells via clinically approved retroviral replicating vectors.

Reclassification of ETS Family Transcription Factor Fusions in Pediatric AML Based on Molecular Drivers

Pediatric Acute Myeloid Leukemia (pAML) patients with a fusion involving an E26 transformation-specific (ETS) transcription factor have traditionally been considered high-risk. The most common fusions include ETV6::MNX1 t(7;12)(q36;p13) and FUS::ERG t(16;21)(p11;q22), yet primary fusion alone has proven incapable of predicting response to treatment. Indeed, within the 60 pAML patients with ETS fusions from the Children's Oncology Group (COG) trials AAML0531 and AAML1031, there were 25 unique fusions and diverse outcomes between patients who did share a primary fusion. A molecular based reclassification of ETS fused pAML could prove beneficial in the development of novel therapeutic additions to standard induction. Here, using genetic and RNAseq data from over 1,400 pediatric patients from AAML0531 and AAML1031, we reclassified ETS patients based on oncogenic transcriptional profiles as well as access to hematopoietic stem cell transplant (HSCT) ( Figure 1A). (19/60) patients presented with an enhanced MYC transcriptional signature (p-val &amp;lt; 0.00) independent of fusion partners [EP300::ETV6, ETV6::CCND3, ETV6::FAM133B, ETV6::FOXO1, ETV6::INO80D, ETV6::LMBR1, ETV6::MNX1, EWSR1::FEV, FLI1::IFIT2, FUS::ERG, FUS::FEV, FUS::FLI1]. Median event-free survival (EFS) was 293.5 days; median overall survival (OS) was 620.5 days. Notably, 100% (19/19) of patients with a MYC-driven signature relapsed; of the six patients who received HCST, five died within 3 years of diagnosis. Preliminary in vitro data in ETS cell lines with an enhanced MYC transcriptional signature (YNH-1, TSU-1621) suggests that the BET bromodomain inhibitor JQ1 may dampen MYC and induce anti-proliferative effects. (7/60) patients were defined by an EZH2-driven “immune-cold” signature characterized by global loss of immune receptors. Patients presented at diagnosis with significantly elevated EZH2 and low levels of MHC I and II receptors typically observed at relapse; additionally, there was significant downregulation in T cell and natural killer cell ligands and a 100% failure rate for HSCT. Median EFS was 255 days and median OS was 339 days. We have previously discussed the mechanism of leukemogenesis as well as proposed therapeutic interventions for this subset (Buteyn, ASH 2021). (34/60) patients did not possess either a MYC-driven or EZH2-driven signature. These “other” ETS were instead defined by whether or not the patient underwent HCST. (21/34) patients did not receive HCST and had median EFS and OS of 429 and 1194 days, respectively. The relapsed or refractory rate in this population was still 75%; (8/14) of R/R patients were deceased within three years. The remaining (13/60) ETS patients did receive HSCT in first remission. (11/13) are still alive and at a rate higher than the general pAML population post-HSCT (62.6%). Despite a survival rate at approximately 85%, ‘Other ETS +HSCT’ patients were all still categorized as ‘High Risk’ at the end of AAML1031. Overall, reclassification based on molecular drivers appears to not only be more accurate in predicting relapse and final outcome, but also in proposing novel agents for pAML patients who overwhelmingly do not respond to standard regimens. Reinvigoration of immune recognition by inhibition of EZH2 and/or inhibition of MYC-driven proliferation via BET inhibitors may prove an essential step in setting the stage for successful HSCT for a significant portion of pAML ETS patients.

Expression of CD44 is regulated by ELF3 in 5-FU treated colorectal cancer cells

The development of chemoresistance in colorectal cancer (CRC) cells was usually thought to be inevitable as a result of continuing exposure to chemotherapeutic drugs. The existence of cancer stem cells (CSCs) within CRC tissues was recently suggested to play importance roles for this process. In this study, in order to mimic a dose schedule used in clinic (continuous infusion), low dose of fluorouracil (IC10 of 5-FU) was used to treat CRC cells. Our results showed that the expression of CD44, including some other CSCs markers were all increased after 5-FU treatment. The stemness properties of survived CRC cells were also observed to be enhanced. RNA-seq analysis revealed that ELF3, one of the members of ETS (E26 transformation-specific) transcription activator family, was increased along with CD44 after 5-FU treatment of CRC cells. Results from dual-luciferase reporter assay revealed that the transcription of CD44 could be activated by ELF3 in CRC cells. The induced CD44 expression in 5-FU treated CRC cells could also be decreased after the expression of ELF3 was inhibited. Moreover, it could be observed that the expression of ELF3 is significantly higher in CD44+ CRC cells. Taken together, our results suggested that CD44 expression might be regulated by ELF3 and could be induced after 5-FU treatment of CRC cells. Inhibition of ELF3 might be a promising treatment method when it was used in combination with chemotherapeutics to overcome chemoresistance formation during CRC treatment in clinic.

The Small-Molecule E26-Transformation-Specific Inhibitor TK216 Attenuates the Oncogenic Properties of Pediatric Leukemia.

The E26-transformation-specific (ETS) transcription factors regulate multiple aspects of the normal hematopoietic system. There is an increasing body of evidence suggesting aberrant ETS activity and its contribution to leukemia initiation and progression. In this study, we evaluated the small-molecule ETS inhibitor TK216 and demonstrated its anti-tumor activity in pediatric leukemia. We found TK216 induced growth inhibition, cell cycle arrest and apoptosis and inhibited the migratory capability of leukemic cells, without significantly inhibiting the cell viability of normal blood mononuclear cells. Priming the leukemic cells with 5-Azacitidine enhanced the cytotoxic effects of TK216 on pediatric leukemia cells. Importantly, we found purine-rich box1 (PU.1) to be a potential target of TK216 in myeloid and B-lymphoid leukemic cells. In addition, TK216 sharply decreased Mcl-1 protein levels in a dose-dependent manner. Consistent with this, TK216 also potentiated the cytotoxic effects of Bcl-2 inhibition in venetoclax-resistant cells. The sustained survival benefit provided to leukemic cells in the presence of bone-marrow-derived conditioned media is also found to be modulated by TK216. Taken together, our data indicates that TK216 could be a promising targeted therapeutic agent for the treatment of acute myeloid and B-lymphoid leukemia.

ETV5 facilitates tumor progression in head-neck squamous cell carcinoma.

E26 transformation-specific (ETS) factors have emerged as key mediators underlying human tumorigenesis. Here, we sought to characterize the expression pattern, biological roles, and clinical significance of ETS Variant Transcription Factor 5 (ETV5) in head neck squamous cell carcinoma (HNSCC). ETV5 expression pattern in HNSCC was determined by bioinformatics interrogations and immunohistochemical staining in primary samples. The associations between its abundance with clinicopathological parameters, and patient survival were evaluated. Colony formation, CCK-8, flow cytometry, wound healing, and Transwell invasion assays, as well as xenograft models, were utilized to determine the phenotypic changes after ETV5 silencing in vitro and vivo. The potential binding of ETV5 in the Slug promoter was determined by ChIP-qPCR. ETV5 was significantly overexpressed in HNSCC samples. Its overexpression is significantly associated with aggressiveness features and reduced survival. ETV5 knockdown significantly inhibited cell proliferation, migration, invasion, and induced apoptosis in vitro, and impaired tumor growth in vivo. Moreover, ETV5-activated Slug transcription by binding its promoter region in HNSCC cells. Patients with ETV5highSlughigh had the worst survival across multiple HNSCC cohorts. Our findings reveal that ETV5 serves as a novel prognostic biomarker and putative oncogene for HNSCC progression likely by activating Slug transcription.

Unravelling the Role of P300 and TMPRSS2 in Prostate Cancer: A Literature Review.

Prostate cancer is one of the most common malignant diseases in men, and it contributes significantly to the increased mortality rate in men worldwide. This study aimed to review the roles of p300 and TMPRSS2 (transmembrane protease, serine 2) in the AR (androgen receptor) pathway as they are closely related to the development and progression of prostate cancer. This paper represents a library-based study conducted by selecting the most suitable, up-to-date scientific published articles from online journals. We focused on articles that use similar techniques, particularly those that use prostate cancer cell lines and immunohistochemical staining to study the molecular impact of p300 and TMPRSS2 in prostate cancer specimens. The TMPRSS2:ERG fusion is considered relevant to prostate cancer, but its association with the development and progression as well as its clinical significance have not been fully elucidated. On the other hand, high p300 levels in prostate cancer biopsies predict larger tumor volumes, extraprostatic extension of disease, and seminal vesicle involvement at prostatectomy, and may be associated with prostate cancer progression after surgery. The inhibition of p300 has been shown to reduce the proliferation of prostate cancer cells with TMPRSS2:ETS (E26 transformation-specific) fusions, and combining p300 inhibitors with other targeted therapies may increase their efficacy. Overall, the interplay between the p300 and TMPRSS2 pathways is an active area of research.

DIPG-20. DELINEATING MEDIATORS OF ONCOGENESIS IN FOXR2-EXPRESSING DIFFUSE MIDLINE GLIOMAS

Abstract BACKGROUND Diffuse midline gliomas (DMGs) are a universally fatal brain tumor of childhood. While histone mutations are a critical tumor initiating event, they are insufficient to drive gliomagenesis. Histone mutations co-occur with somatic alterations in other pathways including TP53, MAPK, and MYC signaling. However, the mechanisms through which these pathways are activated have not been fully elucidated. METHODS We applied an integrative approach using transcriptomics, epigenetics, proteomics, in vitro cancer models, and in vivo mouse models to systematically evaluate how FOXR2 mediates gliomagenesis. RESULTS We have recently found that a subset of DMGs aberrantly express FOXR2, a forkhead transcription factor. FOXR2 is both sufficient to enhance tumor formation, and necessary for FOXR2-expressing DMGs. While FOXR2 indeed enhances MYC protein stability, FOXR2 exerts oncogenesis through MYC-independent functions and specifically hijacks E26-transformation specific (ETS) transcriptional circuits and FOXR2 DNA-binding is highly enriched at ETS motifs. We have performed proteomic and phospho-proteomic analysis of FOXR2-expressing human neural stem cells to identify proteins and phospho-sites that are highly enriched in FOXR2-expressing cells. CONCLUSION Taken together, this study elucidates how FOXR2 interacts with ETS transcription factors to mediate oncogenesis in FOXR2-expressing diffuse midline gliomas.

ETS transcription factors: Multifaceted players from cancer progression to tumor immunity.

The E26 transformation specific (ETS) family comprises 28 transcription factors, the majority of which are involved in tumor initiation and development. Serving as a group of functionally heterogeneous gene regulators, ETS factors possess a structurally conserved DNA-binding domain. As one of the most prominent families of transcription factors that control diverse cellular functions, ETS activation is modulated by multiple intracellular signaling pathways and post-translational modifications. Disturbances in ETS activity often lead to abnormal changes in oncogenicity, including cancer cell survival, growth, proliferation, metastasis, genetic instability, cell metabolism, and tumor immunity. This review systematically addresses the basics and advances in studying ETS factors, from their tumor relevance to clinical translational utility, with a particular focus on elucidating the role of ETS family in tumor immunity, aiming to decipher the vital role and clinical potential of regulation of ETS factors in the cancer field.

Elucidating Inflammation-induced Cell Fate Decisions in Primary Human Tregs

Abstract Adoptive regulatory T-cell (Treg) therapy is an emerging therapeutic paradigm for promoting immune tolerance in transplant and autoimmune disease settings. Prior investigations demonstrate that murine Tregs can undergo epigenetic reprogramming within chronically inflamed tissue environments, resulting in acquisition of proinflammatory functions and the capacity to exacerbate tissue damage. Despite the ramifications of Treg lineage decommitment for cell therapy applications, inflammation-induced human Treg cell fate decisions remain poorly understood. Here, we present a robust in vitromodel of IL6, IL1β, and IL23-driven Treg instability characterized by progressive FOXP3 and HELIOS downregulation, FOXP3conserved non-coding sequence (CNS)2 enhancer re-methylation, diminished in vitrosuppressive function, and elevated proinflammatory cytokine expression. To gain insight into the gene regulatory networks enabling the loss of Treg identity, we generated single-cell transcriptomic and chromatin accessibility profiles of primary human Tregs maintained in the presence or absence of IL6, IL1β, and IL23. Unsupervised clustering revealed a dysfunctional Treg population with an epigenetic signature consistent with murine Treg to “exTreg” conversion, including altered chromatin accessibility at the IFNγ, IL17A, and FOXP3CNS2 loci. Inference of transcription factor (TF)-associated changes in chromatin accessibility indicated a key role for E26 transformation-specific (ETS) family members. Ongoing experiments aim to identify specific TF modules that can be targeted to better safeguard the function and stability of Treg therapeutics.

Abstract 3562: Dissecting mechanisms underlying FOXR2-mediated gliomagenesis in diffuse midline gliomas

Abstract Background: Diffuse midline gliomas (DMGs) are a universally fatal brain tumor of childhood. While histone mutations are a critical tumor initiating event, they are insufficient to drive gliomagenesis. Histone mutations co-occur with somatic alterations in other pathways including TP53, MAPK, and MYC signaling. However, the mechanisms through which these pathways are activated have not been fully elucidated. Methods: We applied an integrative approach using transcriptomics, epigenetics, proteomics, in vitro cancer models, and in vivo mouse models to systematically evaluate how FOXR2 mediates gliomagenesis. Results: We have recently found that a subset of DMGs aberrantly express FOXR2, a forkhead transcription factor. FOXR2 is both sufficient to enhance tumor formation, and necessary for FOXR2-expressing DMGs. While FOXR2 indeed enhances MYC protein stability, FOXR2 exerts oncogenesis through MYC-independent functions and specifically hijacks E26-transformation specific (ETS) transcriptional circuits and FOXR2 DNA-binding is highly enriched at ETS motifs. We have performed proteomic and phospho-proteomic analysis of FOXR2-expressing human neural stem cells to identify proteins and phospho-sites that are highly enriched in FOXR2-expressing cells. Conclusion: Taken together, this study elucidates how FOXR2 interacts with ETS transcription factors to mediate oncogenesis, and further highlights a role for FOXR2 in activating ETS and MAPK signaling. Citation Format: Jessica W. Tsai, Paloma Cejas, Marissa Coppola, Dayle K. Wang, Smruti Patel, David W. Wu, Phonepasong Arounleut, Xin Wei, Ningxuan Zhou, Sudeepa Syamala, Frank P. Dubois, Kristine Pelton, Jayne Vogelzang, Cecilia Sousa, Audrey Baguette, Xiaolong Chen, Alexandra L. Condurat, Sarah E. Dixon-Clarke, Annarah Charles, Kevin N. Zhou, Sophie D. Lu, Elizabeth M. Gonzalez, Madison S. Chacon, Jeromy J. Digiacomo, Rushil Kumbhani, Dana Novikov, Maria Tsoli, David S. Ziegler, Uta Dirksen, Natalie Jager, Gnana Prakash Balasubramanian, Christof M. Kramm, Michaela Nathrath, Stefan Bielack, Suzanne J. Baker, Jinghui Zhang, James M. McFarland, Gad Getz, Francois Aguet, Nada Jabado, Olaf Witt, Stefan M. Pfister, Keith L. Ligon, Volker Hovestadt, Claudia Kleinman, Henry Long, David T. Jones, Pratiti Bandopadhayay, Timothy N. Phoenix. Dissecting mechanisms underlying FOXR2-mediated gliomagenesis in diffuse midline gliomas. [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 3562.

Abstract 1435: A GABP dominant negative approach to targeting tumor cell immortality

Abstract Immortality is a hallmark of human cancer cells and therapeutic reversal is of great interest. Telomerase Reverse Transcriptase promoter (TERTp) mutations reactivate TERT expression, the rate limiting step in telomerase activity and cellular immortality. While prior telomerase blocking therapies lack tumor selectivity and were poorly tolerated, TERTp mutations and their regulation offer a unique opportunity for tumor specific reversal of cellular immortality. TERTp mutations are the most common non-coding mutation across all cancers, including glioblastoma (GBM), melanoma, urothelial carcinoma, and many others. The mutations generate a de novo E26 Transformation Specific (ETS) binding motif that recruits the GA-Binding Protein (GABP) multimeric complex to reactivate TERT expression. While GABP can form both a dimeric and tetrameric complex, we found that the tetrameric complex is responsible for reactivation of the mutant TERTp, suggesting selectively targeting the tetramer may induce telomere shortening and tumor cell death. However, through knocking out the tetramer, we found that the GABP dimer is sufficiently upregulated to maintain TERT expression. In the absence of the dimer and the tetramer isoform, many tumor cells senesce or undergo cell death. However, some escape this fate via upregulation of a second tetramer forming GABP paralogue that maintains TERT expression. Therefore, we devised a transactivation domain null GABP subunit that we hypothesized would act in a dominant negative manner to block the GABP dimer and both GABP tetramers. Introduction of the dominant negative construct into TERTp mutant GBM, meningioma, medulloblastoma, oligodendroglioma, and urothelial carcinoma cells significantly reduced TERT expression while not altering expression in TERTp wildtype GBM cells. Furthermore, the dominant negative is able to shorten telomere length in TERTp mutant GBM cells. While therapeutic targeting of the three GABP complexes seems particularly challenging, our initial dominant negative appears to do so. Ultimately the dominant negative could be delivered directly into tumors via clinically approved viral delivery systems such as retroviral replicating vectors. Citation Format: Nicholas O. Stevers, Sara A. Collins, Samuel H. Wu, Noriyuki Kasahara, Joseph F. Costello. A GABP dominant negative approach to targeting tumor cell immortality [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1435.

Abstract 1474: Hippo-mediated control of the mutant TERT promoter via MYC and GABP

Abstract Most cancers achieve replicative immortality through reactivation of telomerase reverse transcriptase (TERT), the rate limiting subunit in telomerase activity. Tumors from more than 50 distinct cancer types reactivate TERT expression via mutations in the TERT promoter. Understanding how the mutations lead to activation and immortality is a central question in cancer research. Oncogenic signaling pathways including EGFR/AMPK, MAPK, and C-MYC/ASL, have been linked to telomere maintenance via their regulation of the mutant TERT promoter. Two mutually exclusive point mutations in the TERT promoter generate a de novo E26 Transformation Specific (ETS) binding motif that recruits the GA-Binding Protein (GABP) multimeric complex to reactivate TERT expression (Bell et al, Science 2015). Recruitment of GABP to the mutant TERT promoter facilitates the recruitment of C-MYC to the promoter (Shi et al, Mol. Cell 2022), which aids in transcriptional activation. The Hippo pathway plays a key role in development, organ size determination, and homeostasis, and has been found dysregulated in numerous cancer types. GABP is a member of the Hippo pathway, with GABP activating the promoter of the Hippo transcriptional effector Yes-associated protein (YAP1) and the Hippo pathway core kinases stimulating GABP nuclear exit (Wu et al., Cell Reports 2013). We have found that YAP and its paralogue transcriptional coactivator with PDZ-binding motif (TAZ) are linked to mutant TERT promoter activation in glioblastoma via transcriptional activation of both GABPA and MYC. These observations suggest the Hippo pathway supports tumor immortality in glioblastoma. While immortality has proven to be an elusive target, further investigations of the signaling networks that converge on the activation of the mutant TERT promoter may reveal therapeutic targets that block tumor growth and have secondary benefit by their impact on tumor immortality. Citation Format: Nicholas O. Stevers, Andrew Mancini, Joseph F. Costello. Hippo-mediated control of the mutant TERT promoter via MYC and GABP [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 1 (Regular and Invited Abstracts); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(7_Suppl):Abstract nr 1474.

Nifuroxazide Activates the Parthanatos to Overcome TMPRSS2:ERG Fusion-Positive Prostate Cancer.

Fusion of the E-26 transformation-specific (ETS)-related gene (ERG) with transmembrane serine protease 2 (TMPRSS2) is a crucial step in the occurrence and progression of approximately 50% of prostate cancers. Despite significant progress in drug discovery, ERG inhibitors have yet to be approved for the clinical treatment of prostate cancer. In this study, we used computer-aided drug design (CADD)-based virtual screening to screen for potential inhibitors of ERG. In vivo and in vitro methods revealed that nifuroxazide (NFZ) inhibited the proliferation of a TMPRSS2:ERG fusion-positive prostate cancer cell line (VCaP) with an IC50 lower than that of ERG-negative prostate cancer cell lines (LNCaP, DU145, and WPMY cells). Poly [ADP-ribose] polymerase 1, the critical mediator of parthanatos, is known to bind ERG and is required for ERG-mediated transcription. NFZ blocked this interaction and overly activated PARP1, leading to cell death that was reduced by olaparib, a PARP1 inhibitor. These results show that NFZ inhibits ERG, leading to parthanatic cell death.